Poster Session Only
A review of the basic structure of passive continental margins suggests that their general movement along the margin is down slope and basinward. In the case of the northern Gulf of Mexico, the continental margin extends from the fall line at Little Rock, Arkansas, to the Gulf’s abyssal plain. This margin represents an overall dip-oriented lateral distance of some 10 degrees latitude, circa 1200 km. It descends from continental elevations of ca. 500 m to submarine depths of greater than 3 km.
As the rifting basin rapidly evolved during the tectonic subsidence phase, various rifted basement blocks have subsided and rotated basinward and seafloor spreading and plate tectonics have determined subsidence rates. Tectonic motions within the overlying sediment cover are primarily extensional, as shown by listric faulting. Localized compression occurs at the foot of the listric faulting. Dynamic migration of shale or salt serves as a “tectonic escape” moving basinward and down slope. These motions range from margin spanning, to regional, to local, to microscopic; the motions occur on time scales varying from instantaneous to geologically slow.
The second-order sedimentary units, determined from sequence and seismic stratigraphy, record characteristics of the deposition itself. The sediments at present occur at greater depths in the subsurface than their original site of deposition as a result of subsidence and lateral migration.
This paper suggests that “margin tectonics” along passive continental margins cause general down slope movements of debris, due to both subsidence and lateral motion.